(Adapted from Applicant's Abstract) PI T. Aldrich will examine vaso- occlusion in the lung using the hypothesis is that polymer formation in regions of alveolar hypoxia impairs deformability of sickle cells perfusing such regions and, coupled with hypoxia-induced regional pulmonary arteriolar vasoconstriction, promotes entrapment of the abnormal erythrocytes. In the rat model he will evaluate the relative importance of mechanical deformability versus hypoxic vasoconstriction and in the transgenic mouse he will examine the role of agents promoting adhesion and those affecting vascular tone as well as the effect of bone marrow embolism and phospholipase A2 levels.